1. Field of the Invention
The present invention relates to a supporter for a bud of plant, a tree and a cut flower or a supporter which is suited for growing of a plant, and more in detail relates to a polyisocyanurate foam having open-cell suited for a supporter to fix and support a plant which has an improved specific property.
2. Description of the Prior Art
It is well known that a polyurethane foam is used a supporter of plant. For instance, a hard type polyurethane foam is used as a supporter for a growing medium of plant such as a planted bud or a planted cutting and a cut flower, and a soft type polyurethane foam is used as a nursery sheet for growing a vegetable plant such as a leek, a lettuce or a spinach or a flower such as tulip.
The structural feature of the conventional soft type polyurethane foam is mainly composed by polyalkylene ether bond or polyester bond, which has an adequate elasticity and a hydrophilic and water absorption feature caused by ether bond and ester bond. However, said soft type polyurethane foam is too soft to support a tall plant such as a plant which bears fruit, such as a tomato, therefore is not on the market for a tomato plant. Further, since the soft type polyurethane foam has elasticity, it has a problem of difficulty to separate the root of plant from the foam when it is applied for example to the growing of a leek. Many trials to develop a hard type polyurethane foam of low elasticity having open cell and to use it as a nursery sheet for plants are carried out, whose open-cell can be broken with the growth of root and do not prevent the growth of plant root.
In general, the molecular weight of polyol which composes a hard type polyurethane foam is smaller than that of polyol which composes a soft type polyurethane. Further, since the hard type polyurethane foam has a multi-functional property, the reactivity with isocyanates is very rich and easily forms closed cell, therefore, it is very difficult to prepare a hard type foam which has open cell. For the preparation of a hard type polyurethane foam for a nursery sheet, it is necessary to form open cell to improve water absorption and water holding ability. These prior arts are disclosed in Japanese Patent Laid-open publication 46-741, Japanese Patent Laid-open publication 48-25098, Japanese Patent Laid-open publication 49-63796, Japanese Patent Laid-open publication 49-97897, Japanese Patent Laid-open publication 2-14209 and Japanese Patent Laid-open publication 2-212511.
In the document of Japanese Patent Laid-open publication 46-741, polyol whose molecular weight is smaller than 500 and polyol of high molecular weight whose molecular weight is 500 to 5000 are used a polyol, isocyanate index is restricted to 20 to 80, the reactivity difference of polyol and isocyanate index is set up at low level of 20 to 80, an open-cell structure is obtained by preventing the bridging reaction and a hydrophilic feature is achieved by matching OH group remaining in view of the low isocyanate index.
However, referring to the foam obtained by said method, proportion of open-cell is low, and so the water absorption is low level of 51 to 75%. Further, there remains elasticity caused by lack of bridging bonds and hard segments. That is, since the obtained foam has problems of lack of hardness and when it is used to support a planted bud or a planted cutting or a cut flower, it is very hard to be inserted. This problem is remarkable for a flower of slender stalk such as a baby's breathe or a flower of soft and thick stalk such as a gerbera.
Japanese Patent Laid-open publication 48-25098, discloses a technique to prepare a hydrophilic foam with open-cell. Tertiary amine polyol which are initiated by amine compound is used as a part of polyol to utilize the reactivity difference of polyols and isocyanate index is restricted to lower level of 50 to 90 similarly to Japanese Patent Laid-open publication 46-741. However, the proportion of open-cell is low and so the water absorption is low. Therefore, the problems of elasticity caused by lack of bridging bonds and hard segments remains, and as a result it has a similar problem of lack of hardness; consequently it is very hard to insert a flower of slender stalk or a flower of soft and thick stalk.
Japanese Laid-open publication 49-63796, disclose a method to prepare a compressed foam which restores to its original size by water swelling. This method uses a low molecular weight polyol and a specific modified low reactive aliphatic isocyanate compound. However, the proportion of open-cell of the obtained foam is low, and the foam has an elastic feature caused by isocyanate compound which is used as a starting material, and has a similar problem, that is, a lack of hardness, consequently the foam is very hard to insert a flower of slender stalk or a flower of soft and thick stalk.
Japanese Patent Laid-open publication 49-97897, discloses a foam prepared using a tertiary amine polyol, a polyol which does not possess tertiary amino group and an emulsifier under the condition of especially low isocyanate index of 55 to 70%.
This foam also utilizes the reactivity difference of polyols and low isocyanate index to form an open-cell, however, elasticity caused by a lack of bridging bonds and hard segments remain, and it has a similar problem which includes lack of hardness, consequently, it is very hard to insert a flower of slender stalk or a flower of soft and thick stalk.
The foam disclosed in the document of Japanese Patent Laid-open publication 2-14209 is a foam which is prepared by using a specific amine polyol and a monoalkylylether polyol of polyethylene glycol and restricting the isocyanate index to the limits of 25 to 90%. This foam is also combining the reactivity difference of polyols, lower bridging bonds proportion by mono-ol and lower bridging bonds proportion by isocyanate index. Therefore, this foam has similar problems to formerly mentioned foams, namely lack of open-cell, elasticity and lack of hardness.
The foam disclosed in the document of Japanese Patent Laid-open publication 2-212511 uses as least two kinds of polyol and prepares an open-cell foam under the presence of acid, however, the proportion of open-cell is low and consequently the water absorption is not so high. Further, the obtained foam lacks hard segments and has an elasticity. Namely it lacks hardness and has a similar problem, consequently, it is very hard to insert a flower of slender stalk or a flower of soft and thick stalk.
As mentioned above, the proportion of open-cell of conventional foam for fixing and supporting plant is low and has appropriate elasticity. Therefore, although the hydrophilicity of the foam is sufficient, the water absorption is low, and the foam is extended when the plant is inserted. That is, the inserting of plant is not uniform buckling against uniform pressure, and concretely it is very difficult to insert a plant of soft stalk.
As clearly understood from the documents mentioned above, since the conventional hard type polyurethane foams of hydrophilic open-cell have a problem of lack of water absorbency and lack of easily inserting, it is not practically applied as a supporter for cut flower, and so the usage of it is restricted in a nursery sheet for a rice plant and a spinach. The market of the supporter for cut flower is almost fully occupied by a phenol foam which has a good easily inserting property. Further, the conventional hydrophilic hard type open-cell polyurethane foam have problems of lack of water absorbency and prevention of root growth, the current market is mainly occupied by a phenol foam or a rock wool.
Concerning the above mentioned problems which conventional hard type polyurethane foam, an object of this invention is to provide a hard type open-cell foam which is good at water absorbing rate and capacity, and a good easily inserting ability for a flower of slender stalk or a flower of soft and thick stalk, further have a fixing and supporting ability. Furthermore, another object of this invention is to provide a hard type open-cell foam which has a good ability to support a plant, can easily be broken along with the growth of a plant root and can easily be broken after use, and further has a good water absorbing ability and a big water holding capacity.
Since the conventional foam used in this field is prepared by utilizing the reactivity difference of polyols and lower isocyanate index, the foam of uniform and perfect open-cell can not be obtained, and the residue of independent cells generates buoyancy and prevents the foam from sinking into water, consequently causes a lack of water absorbing capacity. And, since the foam lacks of bridging bonds and hard segments because of lower isocyanate index, it remains elastic, lacks hardness and ease of breaking and has a problem of being difficult for inserting of a flower of slender stalk or a flower of soft and thick stalk. Therefore, still another object of this invention is to solve above-mentioned problems, further, to provide a foam for fixing and supporting a plant which does not use a fulon type foaming agent and an organic solvent different from the preparation method of a phenol foam.
Furthermore, since the phenol foam is foamed and hardened by acid catalyst, pH value is low and is not suited as the supporter for a cut flower, a planted cutting or a planted bud. To avoid said problem, it is necessary to wash the foam by fresh water before actual use. This procedure is called "removing harshness", and if this "removing harshness" procedure is abbreviated, the life of a cut flower becomes very short.
This invention provides a foam for fixing and supporting a plant which does not need a washing procedure by water.